well the average age for walking is 18 months old, even though a lot of children walk sooner than that. I would keep trying with him like holding his hands and helping him walk, but if you are concerned, I would speak with his doctor and maybe he/she can give you some pointers/advice on what to do.
Some children are later than others the fact he stands is a good sign does he sit up on a chair okay?, it may be a good idea to get him checked out just in case .